| First | Nothing — cycle the tank |
| Then | Clean-up crew |
| Next | Hardy, peaceful fish |
| Last | Aggressive/territorial fish |
| Golden Rule | Slowly — a few additions at a time |
Overview
The order you add livestock matters as much as what you add. Stock too fast and you overwhelm the biological filter (ammonia spike); add aggressive fish too early and they claim the whole tank and bully later arrivals. A sensible stocking order keeps the tank cycling smoothly and the peace intact.
The Order
- Cycle first — no livestock until the tank is cycled.
- Clean-up crew — a few snails/hermits once cycled; they handle early algae and add little waste. See building a clean-up crew.
- Hardy, peaceful fish first — e.g. a clownfish or two; they establish while the biofilter scales up.
- Semi-aggressive/territorial fish last — adding them after peaceful fish are settled reduces bullying, since the newcomers can’t claim an empty tank.
Pace & Quarantine
Add only a couple of animals at a time and wait a few weeks between additions, watching that ammonia/nitrite stay at zero. Quarantine every new fish and acclimate it properly — rushing stocking is how both disease and aggression problems start.
Common Mistakes
Adding a full fish list at once: ammonia spikes and fish die — go slow. Aggressive fish first: they dominate the tank and attack later additions — save them for last. Skipping quarantine because “it’s early”: one un-quarantined fish can seed disease into the whole build.
Related Guides
How to Cycle a New Saltwater Aquarium · Why You Need a Quarantine Tank · Building a Clean-Up Crew · How to Acclimate New Fish
Frequently Asked Questions
What order should I add fish to a reef tank?
Add peaceful, less territorial fish first, such as gobies, cardinals and clowns, and aggressive or territorial ones last, like many tangs, dottybacks and angels, so early fish establish before bullies arrive.
How long should I wait between adding fish?
Usually a couple of weeks between additions, so your biological filter keeps up and you can watch each new fish for disease. Slow stocking is far safer than adding many at once.
When can I add corals?
Once the tank is cycled and parameters are stable, often after the first month or two. Start with hardy softies and LPS while you dial in stability, then move to more demanding corals.